Discharge lamp containing bridge rectifier

ABSTRACT

A self-ballasted discharge lamp comprising an arc tube and an incandescible filament connected in series within an outer jacket includes an integral full wave bridge rectifier. The bridge comprises four diodes and optionally one or two ceramic capacitors which are assembled into a screw base of standard external dimensions. Two diodes are heat sunk directly to the center contact of the base while the other two diodes are heat sunk directly to the base shell. This configuration provides excellent heat dissipation characteristics, mechanical strength and simple assembly.

United States Patent Medendorpvetal. Nov. 6, 1973 54] DISCHARGE LAMPCONTAINING BRIDGE 3,148,305 9/1964 Pearson 1. 315m x RECTIFIER 3,372,3023/1968 Fasola 315/200 R X [75] Inventors: Nicholas W. Medendorp,Willowick; P E R k William H. Lake, Novelty, both of '"f La 6 OhioAsslstant Exammer-Lawrence .1. Dahl Attorney-Ernest W. Legree et al.[73] Assignee: General Electric Company,

, Schenectady, NY. I d [57] ABSTRACT 22 F' M 5 1972 l 1 l e ay Aself-ballasted discharge lamp comprising an arc tube [21] App]. No.:250,646 and an incandescible filament connected in series within anouter jacket includes an integral full wave 7 [52] CI 315/200 R 315/5131 5/71 bridge rectifier. The bridge comprises four diodes and [51] IntCl g 37/00 optionally one or two ceramic capacitors which are as- [58]Field I51 71 179 sembled into a screw base of standard external dimen- 3sions. Two diodes are heat sunk directly to the center I contact of thebase while the other two diodes are heat [56] References Cited sunkdirectly to the base shell. This configuration provides excellent heatdissipation characteristics, me- UNITED STATES PATENTS chanical strengthand simple assembly. 3,527,982 7/1968 Lake 315/200 R 2,928,024 3/1960Dawley 315/51 9 Claims, 7 Drawing Figures r M ,4 1 P4 "5 \\\i F A,

53 g, 40 \w' "t 5/ l 52 I 1 l g :s; I. s. 4/ l f I l l 45 1 '46 PATENTEDRUY 6 I975 SHEET 10F 2 PATENTEDunv sum 377L018 SHEETEGF 2 DISCHARGE LAMPCONTAINING BRIDGE RECTIFIER I BACKGROUND OF THE INVENTION tion, we havedisclosed a resistivelyballasted arc lamp 1 which includes an integralfull-wavebridge rectifier. The bridge rectifier converts the A-.C.supply voltage to D.C. and thereby reduces the extinguishing-voltagesince there is no longer the need at every half cycleto establish ascathode the electrode which was anode during the preceding halfcycleDThis in turn permits the use of a higher voltage arc tube and anincrease in the ratio of voltage drop across the arc tube tovoltage dropacross the ballast filament, resulting in increased efficacy. To providea voltage doubling effect for starting the lamp, one or two of thedio'desof the bridge may have a capacitor connected in parallel. Theseare small size capacitors since-they need only provide current enough toignite the discharge and not to maintain the are. When thevoltagedoublingeffect is not needed, the bridge rectifier may also beused along without 'any capacitor.

After ignition of the lamp, the bridge rectifier continues to operatethe lamp or rectified current and the diodes must have current carryingcapacity adequate for this burden. The real difficulty arises from theneed to provide adequate heat-dissipating capacityfor the diodes. Whilesilicon diodes are used *whichcan withstand a higheroperatingtemperaturethangermanium diodes, the problem of assuringadequate heat dissipation in the confined environment of a highintensity discharge lamp whereof both the arcltube and the ballastingfilament areintense sources oflheat, has remained acute.

SUMMARY OF THE INVENTION In accordance with our invention, adequateheatdissipating capacity for the four diodes of the bridge is achievedby heat-sinking one pair of diodes directly to the center contact ofthebase, andheat-sinking'the other pair of diodes directly to'the baseshelLWe have found that such heat sinking may fortuitously be achievedby way of the required electrical connections 1 odes are disposedtransverse to the lamps axis and soldered or brazed with very shortleadsto the end of the base shell. The othersides of the four diodes areconnected together in pairs to form the conjugate output points acrosswhich the arc tube and the ballast im- 2 pedance consisting of anincandescible filament are connected in series. Where a voltage doublingeffect is desired, one or two of the diodes may be paralleled by a smallcapacitor. The assembly of the four diodes, and the capacitors whenused, is potted in an electrical .resin which also serves to holdthe endcontact in the desired spatial relationship relative to the base shell.

In a variant of the design, chip rectifiers are used in place ofdiscrete encapsulated units. The chip rectifiers are stacked between theend contact and the outer face of the base shell with foils inbetween toserve as the conjugate output points. In yet another variant, anintegral assembly composedof a good heat-dissipating substrate in whichchip rectifiers and conductors are embedded is disposedbetweenthe endcontact and the shell of the base.

DESCRIPTION OF DRAWINGS In the drawings wherein like referencecharacters indicate corresponding elements in the several views:

, FIG. 1 showsschematically the circuit interconnections of the arctube, ballast filament and bridge rectifier. 7

'FIG. 2 illustrates a high pressure metal vapor arc lamp whereintheinvention is embodied. in preferred form.

FIG. 3 is an enlarged sectional view of the base showing heat sinking ofthe diodes to the end contact and to the base shell.

v FIG. 4illustrates a base extension collar which increases theseparation betweenthe hot arctube and 'bridgerectifier in the base.

FIGS. 5a and 5b are sidesectional and end views respectively of a baseshowing a semi-integral bridge assembly constituting a variant of theinvention.

FIG. 6 is a side-sectional view of a baseshowing a full integralassemblyofpellet diodes in a heat dissipating substrate.

DESCRIPTION or PREFERRED EMBODIMENTS The inventionis mose useful whenembodied in the base of a self-ballasted highpressure mercury vapor lamp1 as shown in FIGS. land 2. The lamp 1 comprises an outer glass envelopeor. jacket 2 of ovoid shape. The neck 3 of the outer envelopeis closedby the usual re-entrant stem 4 through which extend stiff inlead wires5, 6. The inner arctube 7 of quartz is provided at opposite ends with apair of main discharge supporting electrodes 8, 9 to which connectionsare made by ribbon type inleads sealed throughthe flattened ends of thetube. Eachelectrode comprises a l a springy clamp 14. The are tube issupported in the harness by clamping its flat ends between metal bandsl5, 16 which are welded to single side rod 12.

An incandescibleballast filament 17 is mounted to extend-axiallyalongside the arctube. It is connected to side rod 12 by conductor 18and to electrode 8 by conductor 19; an insulated support wire 20encirclesthe filament near its midpointto provide additional support.Side rod 12 connects main electrode 9 in series with ballast filament 17to inlead 5 while main electrode 8 is connected directly to inlead 6.The outer envelope is filled with a non-reactive gas, suitably nitrogen,to reduce tungsten evaporation from filament 17. A pair of heatreflector discs 21 is mounted in the neck of the outer envelope justbelow the stem. These discs are necessary in the version of the lampintended for base-up operation in order to reduce the temperature of thebase and of the rectifier bridge components mounted within it. Zirconiumgetter rings 22 absorb any deleterious gas, particularly hydrogen,released during operation.

In the illustrated lamp, arc tube 7 contains a charge of mecury and aninert gas such as argon at a pressure below l millimeters of mercury.Alternatively, the lamp may contain metal halides in addition to themercury charge, for instande sodium iodide and other metal halides.Where the arc tube contains sodium iodide, the electron-emittingmaterial used on the electrodes is thorium oxide.

The bridge rectifier comprises diodes D1 to D4 which are preferablysilicon diodes. In one lamp design rated at 120 volts A.C., 300 watts,the diodes are commerically available passivated and glass-encapsulatedsilicon diodes sold by General Electric Company and designated 1N5625.These are axial lead, avalanche type devices rated at 3.0 amperes andhaving a peak inverse voltage rating of 400 volts. As shown in FIG. 3,diodes D1 and D2 are mounted vertically in base 23 and depend below endcontact 24 to which they are brazed or soldered with extremely shortleads. Conveniently, the short leads are passed through holes in the endcontact and the upper face of the end contact is covered with solder 25.Diodes D3 and D4 are mounted horizontally within the circular aperturein the dome end of base shell 26 to which they are soldered or brazedwith extremely short leads. The assembly utilizes essentially zero leadlength for the bridge connections on one side of each one of the fourdiodes and this gives maximum heat transfer to the end contact and screwshall of the base. These parts engage the conductive metal parts of thefixture socket, namely the center contact and shell respectively, andthe arrangement thereby achieves optimum heatsinking capability. The endcontact and base shell are preferably made of brass and the bridge maybe assembled using l percent tin, 85 percent lead solder, which has asolidus temperature of 225C. to make soldered connections. v

In this embodiment, capacitors C1, C2 are connected in parallel with andclose alongside diodes D3 and D4 respectively to provide a voltagedoubling effect at starting. By using two capacitors, pulse transientswhich might damage the diodes are more effectively bypassed. Suitablecapacitors are Sprague disc ceramic capacitors of 0.001 microfaradhaving a breakdown voltage rating of 1000 volts. These are hightemperature capacitors assembled using high melting point solder andhaving an epoxy-dipped outer coating.

The inwardly directed ends of diodes D1 and D3 are joined together toform conjugate point j3, and similarly the inner ends of diodes D2 andD4 are joined together to form conjugate point j4. As illustrated, thediodes are connected for [forward conduction toward conjugate point j3and away from conjugate point j4 so that the former is positive and thelatter is negative. Teflon-coated stranded wires 27, 28 are used to makethe connections between the bridge output points j3, j4 and the lampinleads 4, 5.

After the bridge components have been mounted in place relative to theend contact and shell of the base, the entire assembly is potted using afilled resin 29 which is flame retardant and has good resistance tomechanical and thermal shock. A suitable material is an epoxy resindesignated Scotchcast XRS 192 and sold by, Minnesota Mining andManufacturing Company. The external configuration of base 23 is the sameas that of a conventional (mogul size) base and it fits into the samekind of socket.

In the embodiment of FIG. 2, the base is fitted on the neck 3 of outerbulb 2 which has threads molded into the glass. A convenient way ofassembling the parts is to first solder stranded wires 27, 28 to theouter ends of inleads S, 6 and slip flexible insulating sleeves over thejoints. The base is next twisted counterclockwise about 2 k turnsrelative to the bulb, and then screwed on clockwise until firmly seatedthe twist being simultaneously removed thereby from the stranded wires.If the threads are smeared with a room temperaturesetting cement whichis resistant to high temperatures prior to screwing the base on the neckof the bulb, a very secure fastening is achieved.

The present lamp is intended in part as a replacement for shorter-livedincandescant lamps. In order to perform similarly in the same fixture oroptical arrangement, the effective light-center length of the presentlamp, that is the distance from the end contact of the base to thecenter of the arc tube, may have to be increased to match that of theincandescent lamp which it replaces. As shown in FIG. 4, this may bedone by interposing an insulating collar 30 between outer bulb 2 v andbase 23. The collar may be of phenolic resin and is threaded internallyat 31 to engage the threaded neck 3 of the bulb, and externally at 32 toengage the threaded base. As before, it is desirable to smear thethreads with cement to assure a secure fastening. By increasing theseparation between the hot arc tube and the base, the collar also servesto reduce the temperature of the bridge rectifier components.

Referring to FIGS. 50 and 5b, there is shown a variant which may betermed a semi-integral base-bridge assembly. In place of discreteglass-encapsulated unit, chip rectifiers are used consisting of flatsemiconductor plates provided with solder pads on each face. The chiprectifiers, D1, D3 and D2, D4 are shown in vertically exploded fashion,stacked in pairs above the flat end 40 of base shell 41 on diametricallyopposite sides of a central aperture 42. Conductive foils 43, 44 areinterposed between the chip diodes in each stacked pair and correspondto conjugate output points +j3 and -j4; insulated conductors 45, 46 areattached thereto and pass out through aperture 42. An end plate having araised central portion 47 which serves as an end contact has shoulderportions 48, 49 seated on and soldered to the top face of the upper chipin each stack. Capacitors C1, C2, if used, may be disposed above endplate 40 in the space to each side of the stacked diode chips as shown,or else within the base shell. The entire assembly is desirably pottedin electrical resin (not shown) in similar manner to the construction ofFIG. 3. The stacking of the chip rectifiers between the base shell andthe end contact achieves high heat-dissipating capacity.

while D3 and D4 are embedded in the bottom face. The

diode chips are interconnected into a bridge circuit by conductors 51,52 formed within the beryllium oxide and providing output junctionpoints or terminals +j3 and j4. Integrated circuit unit 50 is seated ontop of flat end 40 of base shell 41 so that diodes D3 and D4 contact thebase shell. Junction points +j3 and j4 overlie central aperture 42 andhave insulated conductors 45, 46 connected thereto. Diodes D1 and D2 arecontacted by shoulder portions 48 and 49 of the end plate whereof theraised central portion 47 serves as end contact. The direct contact ofdiodes D1, D2 to the end contact, and the direct contact of diodes D3,D4 to the base shell assures good heat dissipation. Heat dissipation isfurther enhanced by the fact that all the diodes are embedded in thethermally heat-conductive substrate of unit 50 which is in directcontact with the base shell'and end contact. Capacitors C1, C2 if usedmay be chip capacitors and may also be embedded in the beryllium oxide.The end of the base may be filled out and protected by an electricallyinsulating resin 53.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

l. A dual envelope internally ballasted arc discharge lamp comprising:

an outer vitreous jacket containing an inner arc tube and a ballastimpedance,

a base fastened to said jacket comprising a metal shell having an endface and an end contact mounted thereabove and insulated therefrom,

a rectifier bridge located in said base and comprising four diodes,

two of the diodes having one side connected to the end contact andlocated next thereto for maximum heat transfer thereto,

two of the diodes having one side connected to the base shell andlocated next thereto for maximum heat transfer thereto,

said diodes being paired off with one connected to the end contact andone connected to the base shell in each pair, and the other side of thediodes in said pairs being connected together to provide conjugateoutput points across which said are tube and ballast impedance areconnected in series.

2. A lamp as in claim 1 wherein said diodes are glass encapsulated axiallead silicon diodes and the connections for maximum heat transferutilize a very short lead connected directly to the end contact or tothe base shell.

3. A lamp as in claim 1 including at least one capacitor located in saidbase and connected in parallel with one of said diodes.

4. A lamp as in claim 1 wherein said diodes are chip rectifiers whereofone pair is located in contact with the end contact and another pair islocated in contact with the shell of the base.

5. A lamp as in claim 1 wherein said diodes are chip rectifiers embeddedand interconnected in a unit of electrically insulating but thermallyconducting substrate, said unit being disposed between the end face andthe end contact of said base.

6. A base for an electric lamp comprising:

a metal shell having a substantially flat end face with an aperturetherein,

a metal end contact mounted above said end face and insulated therefrom,

a rectifier bridge in said base comprising four axial vlead glassencapsulated diodes, two of the diodes depending axially below said endcontact and being connected thereto with very short leads for maximumheat transfer thereto,

two of the diodes being located transversely in said aperture and beingconnected with very short leads to the end face of said base shell formaximum heat transfer thereto,

said diodes being paired off with one connected to bridge rectifier andthe end contact and one connected to the base shell in each pair, andthe other side of the diodes in said paris being connected together toprovide conjugate output points.

7. A base including a bridge rectifier as in claim 6 wherein said diodesare potted in an insulating resin serving to hold the end contact spacedand insulated from the base shell.

8. A base including a bridge rectifier as in claim 6 and at least onecapacitor therein connected across one of said diodes.

9. A base including a bridge rectifier as in claim 6 and a pair of smallcapacitors connected across a pair of said diodes for a voltage doublingeffect at starting, and wherein said diodes and capacitors are potted inan insulating resin which serves also to hold the end contact spaced andinsulated from the base shell.

1. A dual envelope internally ballasted arc discharge lamp comprising:an outer vitreous jacket containing an inner arc tube and a ballastimpedance, a base fastened to said jacket comprising a metal shellhaving an end face and an end contact mounted thereabove and insulatedtherefrom, a rectifier bridge located in said base and comprising fourdiodes, two of the diodes having one side connected to the end contactand located next thereto for maximum heat transfer thereto, two of thediodes having one side connected to the base shell and located nextthereto for maximum heat transfer thereto, said diodes being paired offwith one connected to the end contact and one connected to the baseshell in each pair, and the other side of the diodes in said pairs beingconnected together to provide conjugate output points across which saidarc tube and ballast impedance are connected in series.
 2. A lamp as inclaim 1 wherein said diodes are glass encapsulated axial lead silicondiodes and the connections for maximum heat transfer utilize a veryshort lead connected directly to the end contact or to the base shell.3. A lamp as in claim 1 including at least one capacitor located in saidbase and connected in parallel with one of said diodes.
 4. A lamp as inclaim 1 wherein said diodes are chip rectifiers whereof one pair islocated in contact with the end contact and another pair is located incontact with the shell of the base.
 5. A lamp as in claim 1 wherein saiddiodes are chip rectifiers embedded and interconnected in a unit ofelectrically insulating but thermally conducting substrate, said unitbeing disposed between the end face and the end contact of said base. 6.A base for an electric lamp bridge rectifier and comprising: a metalshell having a substantially flat end face with an aperture therein, ametal end contact mounted above said end face and insulated therefrom, arectifier bridge in said base comprising four axial lead glassencapsulated diodes, two of the diodes depending axially below said endcontact and being connected thereto with very short leads for maximumheat transfer thereto, two of the diodes being located transversely insaid aperture and being connected with very short leads to the end faceof said base shell for maximum heat transfer thereto, said diodes beingpaired off with one connected to the end contact and one connected tothe base shell in each pair, and the other side of the diodes in saidparis being connected together to provide conjugate output points.
 7. Abase including a bridge rectifier as in claim 6 wherein said diodes arepotted in an insulating resin serving to hold the end contact spaced andinsulated from the base shell.
 8. A base including a bridge rectifier asin claim 6 and at least one capacitor therein connected across one ofsaid diodes.
 9. A base including a bridge rectifier as in claim 6 and apair of small capacitors connected across a pair of said diodes for avoltage doubling effect at starting, and wherein said diodes andcapacitors are potted in an insulating resin which serves also to holdthe end contact spaced and insulated from the base shell.